In one aspect, the present invention relates to the manufacture of metallic food and beverage cans and more particularly to the manufacture of 2-piece cans via a draw-redraw metal forming process. In another aspect, the present invention relates to the use of an extrusion coated or film laminated plastic/metal/plastic laminate as the can body feed stock in a draw-redraw steel can forming process.
Metallic cans of various types and sizes find widespread commercial use in the packaging of a wide variety of foods and beverages. In such food and beverage packaging usage, it is generally desired to avoid direct contact between the food or beverage to be packaged and the metallic substance from which the container is manufactured. To that end, metallic cans for food and beverage packaging are typically coated on at least their interior surfaces with a coating of a relatively inert organic substance.
Historically, such organic can coatings were typically deposited or applied from relatively low solids organic solvent-based solutions. However, in more recent times, environmental concerns and regulations requiring substantial reductions in airborne emissions from various industrial facilities have prompted a need for can coatings and can coating processes involving substantially less organic solvent usage (and thus substantially less potential for undesired airborne organic solvent emissions) than is normally encountered with the use of said low solids content organic solvent-based coating systems.
In response to the aforementioned environmental concerns and the attendant need for reduced solvent emission, certain waterborne and high solids organic solvent-based can coating compositions have been developed. Unfortunately, while such waterborne and high solids organic solvent-based systems appear to be potentially suitable for use in certain types of can manufacturing operations (e.g., as coatings in the manufacture of 3-piece rolled and seamed cans and in coating the exterior and/or interior surface of preformed aluminum and/or steel cans made by the draw and iron can forming process), they are not generally satisfactory for use in draw-redraw can forming processes in which a pre-coated steel can stock is employed and in which the coating on such can stock is required to withstand rather severe mechanical stresses involved in the can forming operation. Moreover, even the organic solvent or plasticizer based polyvinyl chloride, epoxy and epoxy phenolic systems conventionally employed to prepare can sheet or coil stock for use in draw-redraw can forming operations are somewhat limited in terms of the maximum depth to diameter draw ratio (or severity of draw) which can be tolerated without coating failure.
In view of the foregoing, it is an object of the present invention to provide an improvement in the manufacture of steel food or beverage cans by the draw-redraw process whereby the use of organic solvent-based coatings for the steel feed stock can be substantially reduced or eliminated. In addition, it is also an object of this invention to provide a means by which retortable draw-redraw containers can be manufactured from film laminated or extrusion coated steel sheet material while still maintaining equal or greater depth to diameter draw ratio capability relative to that currently possible using the conventional organic solvent or plasticizer based coating technology.